Circuit Theory: Basic Concepts, Charge, and Passive Elements

Vocabulary practice flashcards covering fundamental electrical quantities, atomic charge properties, and passive circuit elements (resistors, capacitors, and inductors) from Circuit Theory Unit 1.

Electron

A sub-atomic particle carrying a negative charge of $-1.6 \times 10^{-19}\,\text{C}$ that is deflected towards the positive plate in an electric field.

Proton

A sub-atomic particle located in the nucleus with a positive charge equal in magnitude to the charge on an electron, which deflects towards the negative plate in an electric field.

Neutron

An uncharged, electrically neutral sub-atomic particle residing in the nucleus that is more penetrating than an electron or a proton and cannot be deflected by electric or magnetic fields.

Atomic Nucleus

The small central region of an atom where protons and neutrons (nucleons) are closely packed, having an approximate spherical diameter on the order of $10^{-14}\,\text{m}$.

Electric Field

The region in space around a charged body where electric forces can be experienced by other charges, defined such that it exerts an electrostatic force $\mathbf{F}_E = q\mathbf{E}$ on a body of charge $q$.

Law of Conservation of Electric Charge

The principle stating that total electric charge can neither be created nor destroyed, meaning the initial and final values of total charge in any interaction or reaction must be identical.

Dielectric Conduction

The electrical conduction mechanism characteristic of insulators, occurring because electrons are firmly bound to the nucleus and unable to move freely under an applied potential difference.

Conduction Electrons

Loosely bound electrons in metallic conducting materials that are able to move freely within the crystal structure to produce electronic conduction.

Coulomb's Law

A fundamental law stating that the electrostatic force between two stationary charges is directly proportional to the product of charges ($q_1$ and $q_2$) and inversely proportional to the square of their separation distance ($r$): $F_e = k_e \frac{q_1 q_2}{r^2}$.

Coulomb Constant ($k_e$)

The proportionality factor in Coulomb's law defined as $k_e = \frac{1}{4\pi\varepsilon_0}$, with a numerical value of $8.9875 \times 10^9\,\text{N}\cdot\text{m}^2/\text{C}^2$.

Permittivity of Free Space ($\varepsilon_0$)

A fundamental constant representing the capability of a vacuum to permit electric fields, equal to $8.8542 \times 10^{-12}\,\text{C}^2/\text{N}\cdot\text{m}^2$.

Electric Potential ($V$)

A scalar quantity defined as the potential energy per unit charge ($V = \frac{U}{q}$) or the work done per unit charge in moving a charge from infinity to a point ($V = -\frac{W_\infty}{q}$), measured in volts ($\text{V}$) or joules per coulomb ($\text{J}\cdot\text{C}^{-1}$).

Electric Potential Difference ($\Delta V$)

The difference in potential energy per unit charge between two points in an electric field, equal to the negative of the work done by the electrostatic force to move a unit charge: $\Delta V = V_f - V_i = \frac{\Delta U}{q} = -\frac{W}{q}$.

Electronvolt ($\text{eV}$)

A unit of energy defined as the energy gained by an electron accelerated through an electric potential difference of $1\,\text{V}$.

Electric Current ($I$)

The net drift of free charges through a conductor under an electric field, mathematically related to charge $Q$ and time $t$ by $Q = I t$.

Electric Power ($P$)

The time rate of doing work or transferring electrical energy, given by the relations $P = \frac{W}{t} = V I = I^2 R = \frac{V^2}{R}$.

Electrical Resistance ($R$)

The opposition to the flow of electric current offered by a material, given by $R = \frac{\rho l}{A}$, where $\rho$ is resistivity, $l$ is length, and $A$ is cross-sectional area.

Resistor Color Coding Bands

A standardized band system read from left to right where the first two bands represent significant digits, the third is a multiplier ($10^n$), the fourth represents tolerance, and an optional fifth denotes reliability.

Resistor Reliability Band

The fifth band on a precision resistor that provides a statistical indication of the expected failure percentage of components exceeding nominal resistance after $1000\,\text{hours}$ of operation.

Capacitor

A passive circuit component consisting of two conductors separated by a dielectric insulator, designed to store electrical potential energy in an electric field.

Capacitance ($C$)

The ratio of the magnitude of charge on either plate of a capacitor to the potential difference between them: $C = \frac{Q}{V}$, with the SI unit of the farad ($\text{F}$).

Parallel-Plate Capacitor

A basic capacitor structure composed of two parallel conducting plates of equal area $A$ separated by a distance $d$, having capacitance $C = \frac{\varepsilon_0 A}{d}$ in vacuum or air.

Isolated Spherical Conductor Capacitance

The capacitance of a single isolated conducting sphere of radius $R$, given by $C = 4\pi\varepsilon_0 R$, which is entirely independent of the charge on the sphere.

Capacitors in Series

A connection where capacitors carry identical charge and their combined equivalent capacitance is computed using the reciprocal sum: $\frac{1}{C_{\text{eq}}} = \frac{1}{C_1} + \frac{1}{C_2} + \frac{1}{C_3}$.

Capacitors in Parallel

A connection where capacitors experience the same potential difference across their terminals, resulting in an equivalent capacitance equal to their direct sum: $C_{\text{eq}} = C_1 + C_2 + C_3$.

Dielectric Constant ($k$ or $\varepsilon_r$)

The dimensionless ratio of the capacitance of a capacitor filled with a dielectric ($C$) to its capacitance in a vacuum ($C_0$): $\varepsilon_r = \frac{C}{C_0} = \frac{\varepsilon}{\varepsilon_0}$.

Dielectric Strength

The maximum electric field (potential gradient) an insulating material can withstand without electrical breakdown and the passage of a spark.

Energy Density ($u$)

The electrostatic energy stored per unit volume within an electric field, given by $u = \frac{1}{2}\varepsilon_0 E^2$ in free space and $u = \frac{1}{2}k\varepsilon_0 E^2$ in a dielectric.

Inductance

The property of an electrical circuit whereby an electromotive force (emf) is induced by changes in magnetic flux linkages resulting from a changing current, measured in henrys ($\text{H}$).

Inductor

A circuit component typically consisting of a coil of wire wound around an air, iron, or ferrite core designed to oppose changes in circuit current.

Self Inductance ($L$)

The inductive property occurring when an induced electromotive force arises within the very same circuit that carries the changing current.

Mutual Inductance ($M$)

The inductive property whereby an electromotive force is induced in a circuit due to changing magnetic flux produced by a current changing in an adjacent circuit.